BULLETIN 293 



STUDIES IN MILK SECRETION VIII. 



On the Influence of Age on Milk Yield and Butter-Fat Percent- 

 age, as Determined from the 365 Day Records of 

 Holstein-Friesian Cattle.* 



By John W. Gowen. 

 SUMMARY 



This paper presents a study of the relation of age to the 

 milk yield and to the butter-fat percentage of Holstein-Friesian 

 advanced registry cattle for the 365 day test. 



Two thousand, five hundred and eighty-six records of com- 

 plete year test are analyzed in this paper. 



These records show that milk yield rises at an ever de- 

 creasing rate as the age of the cow increases until the age of 

 maximum productivity is reached, from this age of maximum 

 productivity the milk yield declines at an ever increasing rate 

 as age increases. 



The butter-fat percentage for these Holstein-Friesian cows 

 declines slightly as the age of the cow advances. This decline 

 on the average amounts to only 0.150 per cent. Considerable 

 variation on either side of this mean rate of decline is shown 

 by the records. 



The advanced registries for the different associations of 

 stock growers handling the pure breeds of dairy cattle have 

 focused the attention of the milk producers on the well known 

 fact that age plays a very considerable part in the milk yield of 

 a cow during any given lactation. The advanced registry offi- 

 cials have realized the necessity of taking cognizance of this 

 effect of age on milk yield in determining the requirements which 

 must be met by a cow. At the time when these requirements 



*Papers from the Biological Laboratory of the Maine Agricultural 

 Experiment Station, No. 134. 



